diff --git a/CHANGELOG b/CHANGELOG
index c58b26e1ce..c56e892bd6 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,4 @@
+* Ensure with a test that objects in the Pool have __slots__
 * Use bigdecimal tag for XML-RPC
 * Use tuple in Dict value instead of list
 * Do not set record name on title of report get_email
diff --git a/trytond/ir/avatar.py b/trytond/ir/avatar.py
index c1cc8c0616..4245b176b6 100644
--- a/trytond/ir/avatar.py
+++ b/trytond/ir/avatar.py
@@ -32,6 +32,7 @@ FONT = os.path.join(os.path.dirname(__file__), 'fonts', 'karla.ttf')
 
 
 class ImageMixin:
+    __slots__ = ()
     image = fields.Binary(
         "Image", file_id=file_id, store_prefix=store_prefix)
     image_id = fields.Char("Image ID", readonly=True)
diff --git a/trytond/model/avatar.py b/trytond/model/avatar.py
index 78c846f368..9fb7e3e182 100644
--- a/trytond/model/avatar.py
+++ b/trytond/model/avatar.py
@@ -8,7 +8,7 @@ from trytond.pool import Pool
 
 def avatar_mixin(size=64, default=None):
     class AvatarMixin:
-
+        __slots__ = ()
         avatars = fields.One2Many(
             'ir.avatar', 'resource', lazy_gettext('ir.msg_avatars'), size=1)
         avatar = fields.Function(
diff --git a/trytond/tests/mixin.py b/trytond/tests/mixin.py
index e498f45441..6fdd952d11 100644
--- a/trytond/tests/mixin.py
+++ b/trytond/tests/mixin.py
@@ -6,19 +6,19 @@ from trytond.report import Report
 
 
 class TestMixin:
-    pass
+    __slots__ = ()
 
 
 class TestSecondMixin:
-    pass
+    __slots__ = ()
 
 
 class NotMixin:
-    pass
+    __slots__ = ()
 
 
 class ReportMixin:
-    pass
+    __slots__ = ()
 
 
 class DeactivableModelView(DeactivableMixin, ModelView):
diff --git a/trytond/tests/test_tryton.py b/trytond/tests/test_tryton.py
index 1d645a5846..3573f3492c 100644
--- a/trytond/tests/test_tryton.py
+++ b/trytond/tests/test_tryton.py
@@ -744,6 +744,22 @@ class ModuleTestCase(unittest.TestCase):
                 msg="ModelSingleton must appear before ModelSQL in the parent "
                 "classes of '%s'." % mname)
 
+    @with_transaction()
+    def test_pool_slots(self):
+        "Test pool object has __slots__"
+        for type_ in ['model', 'wizard', 'report']:
+            for name, cls in Pool().iterobject(type_):
+                if not isregisteredby(cls, self.module):
+                    continue
+                if getattr(cls, '__no_slots__', None):
+                    continue
+                for kls in cls.__mro__:
+                    if kls is object:
+                        continue
+                    self.assertTrue(hasattr(kls, '__slots__'),
+                        msg="The %s of %s '%s' has no __slots__"
+                        % (kls, type_, name))
+
     @with_transaction()
     def test_buttons_registered(self):
         'Test all buttons are registered in ir.model.button'